Background

Supernumerary nipples are common minor congenital malformations that consist of nipples and/or related tissue in addition to the nipples normally appearing on the chest. Supernumerary nipples are located along the embryonic milk lines. Ectopic supernumerary nipples are found beyond the embryonic milk lines. The embryonic milk line is the line of potentially appearing breast tissue as observed in many mammals. In humans, the embryonic milk line extends bilaterally from a point slightly beyond the axillae on the arms, down the chest and the abdomen toward the groin. It is generally thought to end at the proximal inner sides of the thighs, although supernumerary nipples have been described on the foot.
[1] Supernumerary nipples can appear complete with breast tissue and ducts and are then referred to as polymastia, or they can appear partially with either of the tissues involved.

Supernumerary nipple - Nipple only (the most common supernumerary nipple)

Supernumerary nipple - Areola only (polythelia areolaris)

Patch of hair only (polythelia pilosa)

Although this classification is clear, encountering interchangeable terms and misnomers when dealing with the supernumerary nipple complex is not surprising due to variability in morphologic patterns.

The paucity of descriptions of supernumerary nipples in medical writings is probably due to its relatively minor clinical significance. The occurrence of supernumerary nipples has been documented since Roman times and featured in legends and ethnic mythology prior to that time. Supernumerary nipples, and particularly polymastia, were attributed to increased femininity and fertility. Ancient artists depicted the goddess of Artemis of Ephesus and the Phoenician goddess of fertility, Astrate, like other ancient deities, as having row upon row of breasts on their chests.
[3] Anne Boleyn, the wife of King Henry VIII, was known to have a third breast. Supernumerary nipples in men were a sign of virility and endowed them with divine powers. Nowadays, film stars expose their supernumerary nipples in the cinema with this same effect.
[3]

The first medical report dates back to 1878 when Leichtenstern estimated the prevalence of supernumerary nipples to be 1 in 500 (0.2%).
[4] In recent years, supernumerary nipples and their association with other congenital anomalies and malignancies has been a topic of considerable debate.

Associations with other diseases

Supernumerary nipple features are found in a number of syndromes, but, in most cases, it is probably a chance finding. These syndromes include Turner syndrome, Fanconi anemia, and other hematologic disorders
[5] ; ectodermal dysplasia; Kaufman-McKusick syndrome; Char syndrome; Simpson-Golabi-Behmel syndrome; and epibulbar lipodermoids associated with preauricular appendages syndrome.
[6] Isolated reports have linked supernumerary nipples to a number of other conditions, but in light of the fact that supernumerary nipples occur with a relatively high frequency in the general population, further studies are needed to validate the following associations:

Publications concerning renal and urinary tract involvement in the presence of supernumerary nipple

In 1979, Méhes drew attention to the association of supernumerary nipples and other anomalies.
[7] The claim that 40% of supernumerary nipples investigated also had renal involvement was striking. This figure was later corrected to 23-27%
[8, 9] ; however, more recent studies have not validated this association. In addition to renal and urinary tract malformations, supernumerary nipples have also been reported in association with solid organ malignancies such as renal adenocarcinoma, testicular cancer, prostate cancer, and urinary bladder carcinoma.

Pathophysiology

Saint-Hilaire in 1836 and Darwin in 1871 supported the notion that the supernumerary nipple is an atavistic structure derived from the milk line of mammals. Conceivably, even the ectopic supernumerary nipple falls in line with Darwin's theory of atavism. Supernumerary nipples on the vulva are consistent with the location of breasts in dolphins and whales; whereas, ectopic supernumerary nipples on the back, scapula, and shoulder
[32, 33, 34] are reminiscent of breast tissue in nutria and hutia (rodents).

Between the fourth and fifth weeks of embryogenesis, an ectodermal thickening forms symmetrically along the ventral lateral sides of the embryo. This epidermal ridge extends from the axillary region to the inner side of the thigh to form the embryogenic milk (or mammary) line. During the second and third months of embryonic development, the glandular elements of the breast are formed near the fourth and fifth ribs, with regression of the rest of the thickened ectodermal streaks. In the case of failure of a complete regression, some foci may remain, resulting in a supernumerary nipple. This can develop into a supernumerary complete breast (polymastia) or into any other supernumerary nipple variant according to the Kajava classification.

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Etiology

Most supernumerary nipples are sporadic, although familial cases have been reported, including 1 report of a family who had supernumerary nipples in 4 successive generations. Familial cases are typically inherited in an autosomal dominant fashion with incomplete expressivity.
[35]

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Epidemiology

Frequency

The prevalence of supernumerary nipples varies geographically. The prevalence is 0.22% in a Hungarian population,
[6] 1.63% in African American neonates,
[20] 2.5% in Israeli neonates,
[21] 4.7% in Israeli Arabic children,
[36] and 5.6% in German children.
[29]

Sex

The incidence of supernumerary nipples is similar in males and females. Some studies have supported a slight male predominance with estimates of male-to-female ratio as high as 1.7:1.

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Prognosis

Most isolated supernumerary nipples persist without complication. Ectopic breast tissue can be associated with the same inflammatory and neoplastic conditions that affect normal breast tissue. Ectopic breast tissue does not have an increased malignant potential compared with normal breast tissue.

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Patient Education

Once a supernumerary nipple is diagnosed, inform the parents or the patient that it is a benign skin lesion in an otherwise healthy individual. Patients should be made aware that supernumerary nipples can go through changes like any regular nipple or breast; these changes may be physiological during puberty or pathological, such as inflammation, mastitis, abscess formation, cysts, adenomata, fibroadenoma, carcinoma, melanoma, or Paget disease.

Robert A Schwartz, MD, MPH Professor and Head of Dermatology, Professor of Pathology, Pediatrics, Medicine, and Preventive Medicine and Community Health, Rutgers New Jersey Medical School; Visiting Professor, Rutgers University School of Public Affairs and Administration